This invention is generally directed to photoconductive imaging members employing organic polymers as charge transport components. More specifically, the present invention is directed to layered imaging members with organic charge transport components selected, for example, from N,N-bis(biarylyl)aniline charge transport polymers. The aforementioned charge transport polymers possess a number of advantages including excellent charge transport properties; they are environmentally safe and non-toxic; and their synthesis easily executable by known synthetic processes. In addition, the charge transport polymers of the present invention can be utilized as a single-component transport layer, that is without the presence of a resin binder, in layered imaging devices. Single-component transport layers provide for long-term device, or imaging member stability in that they are devoid of the problem of small molecule crystallization commonly associated with the small molecule-in-binder transport layer counterparts. Furthermore, the charge transport polymers illustrated herein enable photoconductive imaging members that can be selected for electrophotographic imaging and printing processes for an extended number of imaging cycles, while substantially avoiding, or minimizing undesirable charge transport molecule crystallization. The imaging members of the present invention are especially suitable for imaging and printing apparatuses wherein liquid developers are selected since, for example, resin binders may be avoided thereby eliminating the problem of charge transport molecule leaching and bleeding when the said imaging members are in contact with liquid developers. Moreover, the charge transport polymers of the present invention possess good solubility in common organic solvents such as halogenated, especially chlorinated hydrocarbons, tetrahydrofuran, toluene, xylene, and the like, thus permitting improved coatability thereof by various processes such as spray, dip, and draw-down coating techniques. In one embodiment of the present invention the imaging member is comprised of a supporting substrate, a photogenerating layer, and in contact therewith a charge transport layer comprised of the N,N-bis(biarylyl)aniline charge transport polymer of the formulas illustrated herein. The charge transport layer can be located as the top layer of the imaging member, or alternatively it may be situated between the supporting substrate and the photogenerating layer.
The formation and development of electrostatic latent images on the imaging surfaces of photoconductive materials by electrostatic means is well known. Numerous different photoconductive members for use in xerography are known such as selenium, alloys of selenium, layered imaging members comprised of aryl amine charge transport layers, reference U.S. Pat. No. 4,265,990, and imaging members with charge transport layers comprised of polysilylenes, reference U.S. Pat. No. 4,618,551. The disclosures of the aforementioned patents are totally incorporated herein by reference. However, the layered imaging members with transport layers incorporating the N,N-bis(biarylyl)aniline polymers of the present invention are, for example, economically more attractive than, for example, the members of the '790 and '551 patents in respect of material and fabrication costs, and possess the other advantages illustrated herein. More specifically, the N,N-bis(biarylyl)aniline charge transport polymers of the present invention can be synthesized from readily available inexpensive starting materials via known synthetic processes. In terms of photochemical stability, the charge transport polymers of the present invention are superior to polysilylenes, and do not photodegrade when exposed to ultraviolet radiations.
There are also known photoreceptor materials comprised of other inorganic or organic materials wherein the charge carrier generation and charge carrier transport functions are accomplished by discrete contiguous layers. Additionally, photoreceptor materials are disclosed in the prior art which include an overcoating layer of an electrically insulating polymeric material, and in conjunction with this overcoated type photoreceptor there have been proposed a number of imaging methods.
Specifically, layered photoresponsive devices, including those comprised of photogenerating layers and transport layers, are disclosed in U.S. Pat. No. 4,265,990, and overcoated photoresponsive materials containing a hole injecting layer overcoated with a transport layer, followed by an overcoating of a photogenerating layer and a top coating of an insulating organic resin, reference U.S. Pat. No. 4,251,612. Examples of generating layers disclosed in these patents include trigonal selenium and vanadyl phthalocyanine, while examples of the charge transport layer that may be employed are comprised of the aryldiamines as mentioned therein. The '990 patent is of particular interest in that it discloses layered photoresponsive imaging members similar to those illustrated in the present application with the exception that the charge transporting component of the members of the present invention are comprised of charge transport polymers of the formulas illustrated herein. These members can be utilized in electrophotographic methods by, for example, initially charging the member with an electrostatic charge and imagewise exposing to form an electrostatic latent image which can be subsequently developed to form a visible image. Other representative patents disclosing layered photoresponsive devices include U.S. Pat. Nos. 4,115,116; 4,047,949 and 4,081,274.
As a result of a patentability search, there was located (1) U.S. Pat. No. 3,265,496, which discloses triarylamine photoconductive polymers derived from the reaction of functionalyzed vinyl polymers such as iodostyrene with diphenylamine, as described in column 3, lines 19 to 30 of the patent. At least three important differences exist between the polymers of the '496 patent and the polymers of the present invention: (a) the polymers of '496 patent are addition (vinyl) polymers derived by polymer modification of certain functionalized polymers with appropriate diarylamines; the present invention discloses polycondensation polymers which are obtained by polycondensation of appropriate monomers; (b) the '496 patent describes triarylamine polymers in which the triarylamine moieties are covalently linked to the polymer backbones via a single C--C bond; in the present invention, the N,N-bis(biarylyl)aniline charge transport moieties are covalently bonded to the polymer backbones via two C--O bonds; and (c) the polymers of the '496 patent are functionally photoconductive, whereas the polymers of the present invention are non-photoconductive; they are employed as hole transport materials in layered imaging devices; (2) U.S. Pat. No. 4,725,518 which discloses a tertiary amine as a charge transport small molecule, see for example the formula when R.sub.1 and R.sub.2 are polyphenyl and R.sub.3 is aryl; U.S. Pat. No. 3,767,393 which discloses alkylaminoaromatic photoconductors of the formula as illustrated in column 2 (R.sub.1 -N-R.sub.2 -Ar); and (3) U.S. Pat. Nos. 3,567,450; 3,658,520; 4,025,341; 4,540,651; 4,606,988 and 4,769,302. These patents (3) disclose the use of aromatic amine compounds either as hole transport small molecules or as photoconductive compositions, and are accordingly not believed to be similar to the present invention directed to the use of charge transport polymers based on N,N-bis(biarylyl)aniline in layered photoconductive devices.
There is also disclosed in Belgium Patent No. 763,540 an electrophotographic member having at least two electrically operative layers, the first layer comprising a photoconductive layer which is capable of photogenerating charge carriers, and injecting the photogenerated holes into an active layer containing a transport organic material which is substantially non-absorbing in the spectral region of intended use, but which is active and that allows injection of photogenerating holes from the photoconductive layer and allows these holes to be transported through the active layer. The active polymers may be mixed with inactive polymers or non-polymeric materials. Also, there is disclosed in U.S. Pat. Nos. 4,232,102 and 4,233,383, the disclosures of which are totally incorporated herein by reference, the selection of sodium carbonate doped and barium carbonate doped photoresponsive imaging members containing trigonal selenium.
The following patent applications and U.S. Patents are mentioned: (1) U.S. Pat. No. 4,818,650 describes layered imaging members with novel polymeric, hydroxy and alkoxy aryl amines, wherein m is a number of between about 4 and 1,000, reference for example Claims 1 and 2; (2) U.S. Ser. No. 061,247 (now abandoned) and U.S. Pat. No. 4,871,634 illustrate imaging members with novel dihydroxy terminated aryl amine small molecules, reference Claims 1 and 2, for example; (3) U.S. Pat. No. 4,806,444, the disclosure of which is totally incorporated herein by reference, describes layered imaging members with novel polycarbonate polymeric aryl amines, reference Claims 1 and 2, for example; (4) U.S. Pat. No. 4,806,443, the disclosure of which is totally incorporated herein by reference, illustrates novel polycarbonate polymeric amines useful in layered imaging members, reference Claims 1 and 2, for example; and (5) U.S. Pat. No. 4,801,517, the disclosure of which is totally incorporated herein by reference, which discloses imaging members with novel polycarbonate aryl amines, reference Claims 1 and 2, for example.
In U.S. Pat. Nos. 4,869,988 and 4,946,754 entitled, respectively, PHOTOCONDUCTIVE IMAGING MEMBERS WITH N,N-BIS(BIARYLYL)ANILINE, OR TRIS(BIARYLYL)AMINE CHARGE TRANSPORTING COMPONENTS, and PHOTOCONDUCTIVE IMAGING MEMBERS WITH BIARYLYL DIARYLAMINE CHARGE TRANSPORTING COMPONENTS, the disclosures of which are totally incorporated herein by reference, there are described layered photoconductive imaging members with transport layers incorporating biarylyl diarylamines, N,N-bis(biarylyl)anilines, and tris(biarylyl)amines as charge transport compounds. In the above-mentioned patent, there are disclosed improved layered photoconductive imaging members comprised of a supporting substrate, a photogenerating layer optionally dispersed in an inactive resinous binder, and in contact therewith a charge transport layer comprised of the above-mentioned charge transport compounds, or mixtures thereof dispersed in resinous binders.
Examples of specific charge transporting components disclosed in U.S. Pat. No. 4,869,988 include N,N-bis(4-biphenylyl)-3,5-dimethoxyaniline (Ia); N,N-bis(4-biphenylyl)-3,5-dimethylaniline (Ib); N,N-bis(4-methyl-4'-biphenylyl)-3-methoxyaniline (Ic); N,N-bis(4-methyl-4'-biphenylyl)-3-chloroaniline (Id); N,N-bis(4-methyl-4'-biphenylyl)-4-ethylaniline (Ie); N,N-bis(4-chloro-4'-biphenylyl)-3-methylaniline (If); N,N-bis(4-bromo-4'-biphenylyl)-3,5-dimethoxyaniline (Ig); 4-biphenylyl bis(4-ethoxycarbonyl-4'-biphenylyl)amine (IIa); 4-biphenylyl bis(4-acetoxymethyl-4'-biphenylyl)amine (IIb); 3-biphenylyl bis(4-methyl-4'-biphenylyl)amine (IIc); 4-ethoxycarbonyl-4'-biphenylyl bis(4-methyl-4'-biphenylyl)amine (IId); and the like.
Examples of specific charge transporting compounds disclosed in U.S. Pat. No. 4,946,754 include bis(p-tolyl)-4-biphenylylamine (IIa); bis(p-chlorophenyl)-4-biphenylylamine (IIb); N-phenyl-N-(4-biphenylyl)-p-toluidine (IIc); N-(4-biphenylyl)-N-(p-chlorophenyl)-p-toluidine (IId); N-phenyl-N-(4-biphenylyl)-p-anisidine (IIe); bis(m-anisyl)-4-biphenylylamine (IIIa); bis(m-tolyl)-4-biphenylylamine (IIIb); bis(m-chlorophenyl)-4-biphenylylamine (IIIc); N-phenyl-N-(4-biphenylyl)-m-toluidine (IIId); N-phenyl-N-(4-bromo-4'-biphenylyl)-m-toluidine (IVa); diphenyl-4-methyl-4'-biphenylylamine (IVb); N-phenyl-N-(4-ethoxycarbonyl-4'-biphenylyl)-m-toluidine (IVc); N-phenyl-N-(4-methoxy-4'-biphenylyl)-m-toluidine (IVd); N-(m-anisyl)-N-(4-biphenylyl)-p-toluidine (IVe); bis(m-anisyl)-3-biphenylylamine (Va); N-phenyl-N-(4-methyl-3'-biphenylyl)-p-toluidine (Vb); N-phenyl-N-(4-methyl-3'-biphenylyl)-m-anisidine (Vc); bis(m-anisyl)-3-biphenylylamine (Vd); bis(p-tolyl)-4-methyl-3'-biphenylylamine (Ve); N-p-tolyl-N-(4-methoxy-3'-biphenylyl)-m-chloroaniline (Vf), and the like.
While imaging members with various charge transporting substances, including the aryl amines disclosed in the above patents, are suitable for their intended purposes, there continues to be a need for improved imaging members, particularly layered members, which are comprised of single-component transport layers based on charge transport polymers, thereby ensuring the long-term stability of the members. Another need resides in the provision of layered imaging members that are compatible with liquid developer compositions. Further, there continues to be a need for layered imaging members wherein the layers are sufficiently adhered to one another to allow the continuous use of such members in repetitive imaging systems. Also, there continues to be a need for improved layered imaging members whose transport layers are devoid of the problems of transport molecule crystallization, bleeding and leaching. Further, there continues to be a need for charge transporting polymers which are also useful as protective overcoating layers, and as interface materials for various imaging members. Furthermore there is a need for charge transport compounds or polymers that are nontoxic, and wherein such members are inert to the users thereof. A further need resides in the provision of novel efficient charge transport polymers which are readily accessible synthetically from inexpensive commercial starting materials.